Russian federal nuclear safety rules and regulations ‘Basic Safety Provisions for Nuclear Power Plants’ (NP-001-15) establish a requirement to complement the safety analysis for a nuclear power plant with estimation of errors and uncertainties in the obtained results. Similar requirements can be found in regulatory documents of nuclear safety authorities in most of the countries with well-developed nuclear programme, as well as in the IAEA document GSR Part 4 ‘Safety Assessment for Facilities and Activities'.

Over the past three decades, the Russian Federation, the same as many other countries, has accumulated a great deal of experience in the application of uncertainty estimation techniques for the results of the calculations performed to demonstrate various aspects of the nuclear plant safety. However, these methods are usually discussed in scientific papers published in journals, or in presentations made at conferences, seminars and meetings, while their actual application in respect of NPP safety documentation is very limited, despite the above requirements enshrined in the nuclear safety authority regulations. This may be caused by the lack of national regulatory documents that would guide the safety documentation authors on how they should fulfil the requirement to estimate errors and uncertainties in the results of computational safety analyses.

With this in mind, the SEC NRS had developed a Nuclear Safety Guide ‘Guidance on Estimation of Errors and Uncertainties in the Safety Analysis for Nuclear Power Plants’ (RB-166-20) that was approved by the Federal Environmental, Industrial and Nuclear Supervision Service in its the order No. 288 of July 30, 2020. 

The RB-166-20 Safety Guide contains the recommendations on estimation of errors and uncertainties in the results of a deterministic safety analysis performed using the software tools to demonstrate safety of a nuclear power plant. Thus, the Federal Environmental, Industrial and Nuclear Supervision Service has become a pioneer in issuing uncertainty estimation recommendations.

Before starting the RB-166-20 development, the authors made an overview of the world's best practices in the assessment of errors and uncertainties in the results of the computational safety analyses for nuclear power plants. The study was carried out by SEC NRS together with the staff of the Institute for Safe Development of Nuclear Power with Russian Academy of Sciences, the National Nuclear Research University ‘MIFI’, and the A.P. Aleksandrov Science and Research Technological Institute which is part of the State Atomic Energy Corporation ‘Rosatom’. Noteworthy is the significant contribution made in the RB-166-20 drafting by the staff of the OKB GIDROPRESS, NIKIET, Afrikantov OKBM, Research Centre ‘Kurchatov Institute’, and VNIIAES.

The RB-166-20 consists of two main sections. The first section provides guidance on accounting for uncertainties in the design safety analysis for a nuclear power plant. The second section gives recommendations for the use of uncertainty evaluation methods. The Annexes to the RB-166-20 contain a block diagram showing the uncertainty estimation process for the results of the computational analysis of the design-basis accidents at a nuclear power plant, and a description of the approach to the assessment of errors and uncertainties in the results of beyond-design-basis accident calculations for nuclear power plants, including severe accidents.

The Safety Guide is meant to be used by the staff of operating organisations, Rostechnadzor divisions, and other institutions conducting activities in the field of nuclear energy.